Let the account holder edit their own profile details

The Profile block is headed "Your profile", but the one person on it you
could not change was yourself: your name, your birth year, and whether you
take lessons yourself were fixed at whatever signup recorded, and correcting
any of them meant asking a studio admin.

A "Your details" section now opens the page, saved through the same
nonce-checked template_redirect post/redirect/get path the child rows use:

- Your name, written to display_name and nickname together, for the reason
  updateChild() does — UserName reads the nickname first, and leaving it
  behind would put the account's email address back on every screen that
  names a person.
- "I take lessons myself", the positive of us_guardian_only. This makes good
  on the claim already in bookableStudents() and the feature doc that a
  guardian-only account can put itself right from the profile page.
- Your birth year, held to the same normaliseBirthYear() rule as every other
  student.

The email is shown but not editable: it is the account's user_login as well
as its address, so changing it stays a studio-side job.

The birth-year field deliberately carries no `required` attribute. It is
asked of a student only, and this page loads no JavaScript, so a
browser-enforced `required` would leave a guardian who books solely for
other people unable to submit the form at all; handleSelf() enforces it
against the checkbox instead. Unticking the box does not clear a stored
birth year — it says who books, not "forget what is on file".

Closes #165

Co-Authored-By: Claude Opus 5 <[email protected]>

tests/Unit/Guardian/GuardianServiceTest.php

@@ -321,6 +321,87 @@ class GuardianServiceTest extends TestCase
         self::assertSame('2015', $this->meta[42][GuardianService::META_BIRTH_YEAR]);
     }
 
+    public function testUpdateSelfRenamesAndStoresTheBirthYear(): void
+    {
+        $this->meta[5][GuardianService::META_GUARDIAN_ONLY] = '1';
+
+        Functions\expect('wp_update_user')
+            ->once()
+            ->with(['ID' => 5, 'display_name' => 'Grace H', 'nickname' => 'Grace H'])
+            ->andReturn(5);
+
+        self::assertNull($this->service->updateSelf(5, 'Grace H', '1984', true));
+
+        self::assertSame('1984', $this->meta[5][GuardianService::META_BIRTH_YEAR]);
+        // Saying they take lessons makes them a bookable student again.
+        self::assertFalse(GuardianService::isGuardianOnly(5));
+    }
+
+    public function testUpdateSelfMarksTheAccountGuardianOnly(): void
+    {
+        Functions\when('wp_update_user')->justReturn(5);
+
+        self::assertNull($this->service->updateSelf(5, 'Grace H', '', false));
+
+        self::assertSame('1', $this->meta[5][GuardianService::META_GUARDIAN_ONLY]);
+    }
+
+    /**
+     * "I only book for other people" says who books, not "forget my birth year" —
+     * ticking the box back on should not have cost them what was on file.
+     */
+    public function testUpdateSelfKeepsAStoredBirthYearWhenTheyAreNoLongerAStudent(): void
+    {
+        $this->meta[5][GuardianService::META_BIRTH_YEAR] = '1984';
+
+        Functions\when('wp_update_user')->justReturn(5);
+
+        self::assertNull($this->service->updateSelf(5, 'Grace H', '', false));
+
+        self::assertSame('1984', $this->meta[5][GuardianService::META_BIRTH_YEAR]);
+    }
+
+    public function testUpdateSelfRejectsABlankName(): void
+    {
+        Functions\expect('wp_update_user')->never();
+
+        self::assertInstanceOf(\WP_Error::class, $this->service->updateSelf(5, '   ', '1984', true));
+    }
+
+    /**
+     * The browser cannot enforce the year conditionally, so the server is the
+     * only thing standing between a student and a nonsense age on their record.
+     *
+     * @dataProvider unusableBirthYears
+     */
+    public function testUpdateSelfRefusesAnUnusableBirthYearFromAStudent(string $submitted): void
+    {
+        Functions\expect('wp_update_user')->never();
+
+        self::assertInstanceOf(\WP_Error::class, $this->service->updateSelf(5, 'Grace H', $submitted, true));
+    }
+
+    public function testAccountHolderReportsTheirOwnDetails(): void
+    {
+        $this->meta[5][GuardianService::META_BIRTH_YEAR] = '1984';
+
+        Functions\when('get_userdata')->justReturn($this->user(5, 'Grace', 'Hopper', email: '[email protected]'));
+
+        self::assertSame(
+            ['name' => 'Grace Hopper', 'email' => '[email protected]', 'birth_year' => '1984', 'is_student' => true],
+            $this->service->accountHolder(5)
+        );
+    }
+
+    public function testAccountHolderReportsAGuardianOnlyAccountAsNotAStudent(): void
+    {
+        $this->meta[5][GuardianService::META_GUARDIAN_ONLY] = '1';
+
+        Functions\when('get_userdata')->justReturn($this->user(5, 'Grace', 'Hopper', email: '[email protected]'));
+
+        self::assertFalse($this->service->accountHolder(5)['is_student']);
+    }
+
     public function testRemoveChildUnlinksAndDeletesAChildWithNoHistory(): void
     {
         $this->guardians->shouldReceive('isGuardianOf')->with(5, 42)->andReturn(true);